<!DOCTYPE HTML>
<html>
	<head>
		<title>拖拽</title>
		<meta charset="utf-8">
		<style>
			#div1{
				width:200px;
				height:200px;
				background: red;
				position: absolute;
			}

		</style>
		<script>
			window.onload=function(){
				var oDiv=document.getElementById('div1');
				var disx=0;
				var disy=0;
				oDiv.onmousedown=function(ev){
					var oEvent=ev||event;
					disx=oEvent.clientX-oDiv.offsetLeft;
					disy=oEvent.clientY-oDiv.offsetTop;
					document.onmousemove=function(ev){
						var oEvent=ev||event;
						
						var l=oEvent.clientX-disx;
						var t=oEvent.clientY-disy;
						if(l<0)
						{
							l=0;
						}
						else if(l>document.documentElement.clientWidth-oDiv.offsetWidth){
							l=document.documentElement.clientWidth-oDiv.offsetWidth;
						}
						if(t<0)
						{
							t=0;
						}
						else if(t>document.documentElement.clientHeight-oDiv.offsetHeight){
							t=document.documentElement.clientHeight-oDiv.offsetHeight;
						}
						oDiv.style.left=l+'px';
						oDiv.style.top=t+'px';
					};
					document.onmouseup=function(){
						document.onmousemove=null;
						document.onmouseup=null;
					};
					return false;
				};
				
			}
		</script>
	</head>
	<body>
		<div id="div1">
		</div>
	</body>
</html>